MALE REPRODUCTIVE TACTICS AND FEMALE CHOICE IN THE SOLITARY, PROMISCUOUS BRIDLED NAILTAIL WALLABY (ONYCHOGALEA FRAENATA)

The genetic mating system of the long-nosed potoroo (Potorous tridactylus) with notes on male strategies for securing paternity

The potoroids are a small group of cryptic macropodoid marsupials that are difficult to directly monitor in the wild. Consequently, information regarding their social and mating systems is limited. A population of long-nosed potoroos (Potorous tridactylus) on French Island, Victoria, was monitored from June 2005 to August 2010. Tissue samples were collected from 32 (19 ♂, 13 ♀) independent potoroos and 17 pouch young. We aimed to determine the genetic mating system and identify patterns of paternity through genotyping individuals at 10 microsatellite loci. Additionally, we investigated the importance of body mass and site residency as strategies in securing paternity. Twelve of the 17 pouch young sampled were assigned paternity with confidence to five males. Multiple pouch young were sampled from two long-term resident females, one of which had 10 pouch young sired by multiple partners, with some repeat paternity, while the other had three young sired by one male, suggesting that the mating system is not entirely promiscuous. Sires were recorded on site for significantly longer periods than non-sires but were not significantly larger than non-sires at conception. This suggests that sires employ strategies other than direct competition, such as scramble competition, to secure paternity in P. tridactylus.

Male-male competition, female mate choice and their interaction: determining total sexual selection

Empirical studies of sexual selection typically focus on one of the two mechanisms of sexual selection without integrating these into a description of total sexual selection, or study total sexual selection without quantifying the contributions of all of the mechanisms of sexual selection. However, this can provide an incomplete or misleading view of how sexually selected traits evolve if the mechanisms of sexual selection are opposing or differ in form. Here, we take a two-fold approach to advocate a direction for future studies of sexual selection. We first show how a quantitative partitioning and examination of sexual selection mechanisms can inform by identifying illustrative studies that describe both male-male competition and female mate choice acting on the same trait. In our sample, the most common trait where this occurred was body size, and selection was typically linear. We found that male-male competition and female mate choice can be reinforcing or opposing, although the former is most common in the literature. The mechanisms of sexual selection can occur simultaneously or sequentially, and we found they were more likely to be opposing when the mechanisms operated sequentially. The degree and timing that these mechanisms interact have important implications for the operation of sexual selection and needs to be considered in designing studies. Our examples highlight where empirical data are needed. We especially lack standardized measures of the form and strength of selection imposed by each mechanism of sexual selection and how they combine to determine total sexual selection. Secondly, using quantitative genetic principles, we outline how the selection imposed by individual mechanisms can be measured and combined to estimate the total strength and form of sexual selection. We discuss the evolutionary consequences of combining the mechanisms of sexual selection and interpreting total sexual selection. We suggest how this approach may result in empirical progress in the field of sexual selection.